Before conducting genetic studies for Craig Packer's Lion project, I examined the genetic history of the Cheetah, whose range once spanned the globe. I was amazed to find that every one of today's 20,000 Cheetahs is genetically almost identical. They descend from survivors of a near-extinction catastrophe that resulted in generations of close inbreeding 10,000 years ago.
These and other species share something important with the Ngorongoro Lions -- a population bottleneck. It creates a shrinking gene pool that leaves fewer and fewer mating partners. What are the genetic implications?
The animals become part of a high stakes poker game -- with a crooked dealer. After beginning with a 52-card deck, the players wind up with, say, five cards that they are dealt over and over.
As they begin to inbreed, congenital effects appear, both physical and reproductive. Often abnomral sperm increase; infertility rises; the birthrate falls. Most perilous in the long run, each animal's immune defense system is weakened.
Thus, even if an endangered species in a bottleneck can withstand whatever human development may be eating away at its habitat, it still faces the threat of an epidemic that could well be fatal to the entire population.
This excerpt originally appeared within Captives in the Wild, a National Geographic article examining the fragmented Lion population within Ngorongoro Crater by Craig Packer, associate professor of biology at the University of Minnesota. Pages 122-136
,
31-10-1996